In Iphone, if no facetime installed in phone can i still use imessage? If can how to activate it?

In Iphone, if no facetime installed in phone can i still use imessage? If can how to activate it?

Facetime is on it automatically, just go into settings and make sure imessage is on, thats all you need to do and just send messages like normal, it converts to imessage if the receiver has iOS device and you both have it on.